The invention relates to a lamp, especially a surgery lamp, with at least two electrical bulbs which can be positioned at the focal point of at least one concave mirror serving as reflector.
In German Gebrauchsmuster G 93 11 156.8 there is disclosed an apparatus for the positioning on alternate sides of at least two bulbs in a predetermined position, especially in a focal point of a lamp having a concave mirror, the bulbs being disposed on an apparatus bearing a bistable mechanical position memory. The apparatus can be shifted automatically upon receiving a signal (bulb failure), whereupon a first bulb is brought away from the focal point and a second bulb is moved into the focal point, circuitry producing the movement being associated with the apparatus.
Even though in this case, when a first bulb as the main bulb fails, an equally strong additional illumination without lateral shifting of the cone of light is made possible by a second bulb as a reserve bulb, the changeover requires a controlling signal which, on the basis of the shifting mechanism, does not bring about a changeover to the reserve bulb without a certain delay. The result is an at least slight time-delay during some operation, which should be prevented if possible (the action of the anaesthetic decreases). In addition, there is possible wear due to natural movement, so that constant inspection of the positioning mechanism is necessary.
The problem for the invention is to offer a lamp with great security against failure, in which a changeover in the event of bulb failure is possible without delay and without substantial variation of the field of illumination; furthermore, it is also to be possible to obtain an elevated brightness by the use of two lamps operated in parallel.
The problem is solved by the invention in that at least two concave mirrors are disposed along a common optical axis with a common direction of light emission, at least one of which is configured as a ring reflector, the concave mirrors having focal points spaced apart from one another on the optical axis, at each of which one bulb is situated as a light producing means.
Advantageous embodiments of the subject of the invention are given in claims 2 to 12.
What proves advantageous, in addition to fast changeover (short changeover duration) is a relatively low liability to phenomena of wear; furthermore, no damage is done to the illuminator by any accidental movement. Thus, in the case of use over long periods little expense is to be expected, since no mechanical wear of any kind takes place.
In a preferred embodiment of the invention the concave mirrors are made substantially axially symmetrical.
Advantageously, at least two concave mirrors form a single common reflector, while at least one concave mirror, configured as a ring reflector, has a central opening which is closed by at least one concave mirror disposed concentrically therein. The use of a one-piece reflector proves especially advantageous. Preferably both concave mirrors of the common reflector are configured each as part of an ellipsoid in which one bulb is used as a light source in a first focal point. The second focal point of the concave mirror configured as a partial ellipsoid is situated at least approximately within the field of illumination. The lamps situated each at different focal points can be switched on individually and independently (i.e., separately from one another).
Preferably both bulbs, seen in the direction of the emission of the light, are provided each with a concave counter-reflector which reflects the radiation issuing frontally along the optical axis in back of the filaments toward the hollow mirror. It proves to be advantageous that no direct radiant heat strikes the illuminated fieldxe2x80x94e.g., the incision produced in the operation on the patient.
In a preferred embodiment of the invention, the reflecting surface of the concave mirror serving as counter-reflector is configured as part of a sphere. The reflecting surface of the concave mirror for the spare lamp can be configured as part of a paraboloid.
The common reflector preferably has a faceted surface on both of the concave mirrors.
Furthermore, the reflecting surface is provided with an interference coating so as to remove any thermal radiation toward the rear of the reflector or of the housing covering it on the back side (i.e., away from the actual illuminated field).
The first bulb serving as the main bulb is disposed on a mounting for displacement along the reflector axis such that its radiation toward the concave mirror of the spare lamp is blocked by a shielding disk between the two bulbs.
A halogen bulb is used with preference as the main lamp, but it is also possible to use a discharge bulb; the second bulb serving as a spare is always in the form of an incandescent or halogen lamp which can be supplied directly from the low-voltage supply main (24 V main) backed by an emergency power supply for operating rooms.
Due to the arrangement of a main bulb and reserve bulb, when a changeover is made, no abrupt change occurs in the illuminated field, such as would be expected with an off-center arrangement of the spare bulb.
The changeover is triggered by a sensor through which the current for the main bulb passes and which in the event of a power interruption produces the switchover by operating a switch means, preferably a relay. A Hall generator is preferably used as the sensor.